So i finally broke doown and started cleaning my garage yesterday. I got about 3 foot up one wall and my pager went off. Smoke filled house possible struture fire. We get on scene and there is no fire in the house so we pull apart the single wall flue pipe to check things out.The metel pipe had about 3/16 oc creasote in it. I started checking the block flue and found at least an inch thick buildup of mostly glazey creasote. I run my arm up through the thimble as far as i could and my fist balled up would barely fit. Remember this is a block flue with clay liners. This was absolutly the worst i had ever seen. No cleanout door on the bottom of it either by the way. So when it is cleaned it will probably fill up to the thimble. Moral of the story clean your flue if nothing else once a year. More is better if unsure. A detail i forgot to mention is that it was a cook stove. No one was hurt so thats good. At least i got out of cleaning my garage. KEEP IT CLEAN.